How to add authentication on reverse proxy where target system don't require.

[#1]

Try to accomplish one use case via Apigee. Let say Our target system doesn't require any username/password or any token to access their API. But I want to create a reverse proxy on their API with a basic credential or token based auth. I want to generate username/password or token on Edge and save it somewhere. Once a client calls my reverse proxy with username/password, Edge will validate it with generated credential and process to target system accordingly.